// 可以加上`match`卫语句(guard)来过滤分支
fn main() {
    let pair = (2, -2);

    println!("Tell me about {:?}", pair);
    match pair {
        // `if`条件部分是一个卫语句
        (x, y) if x == y => println!("These are twins"),
        (x, y) if x + y == 0 => println!("Antimatter, kaboom"),
        (x, _) if x % 2 == 1 => println!("The first one is odd"),
        _ => println!("no correlation")
    }
}
